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TPS62050DGSRG4 Datasheet(PDF) 10 Page - Texas Instruments |
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TPS62050DGSRG4 Datasheet(HTML) 10 Page - Texas Instruments |
10 / 25 page TPS62052, TPS62054 TPS62056, TPS62050, TPS62051 SLVS432E – SEPTEMBER 2002 – REVISED JUNE 2011 www.ti.com APPLICATION INFORMATION Operation The TPS6205x is a synchronous step-down converter that operates with a 850-kHz fixed frequency pulse width modulation (PWM) at moderate to heavy load currents and enters the power-save mode at light load current. During PWM operation the converter uses a unique fast response voltage mode control scheme with input voltage feed forward to achieve good line and load regulation with the use of small ceramic input and output capacitors. At the beginning of each clock cycle initiated by the clock signal (S), the P-channel MOSFET switch is turned on and the inductor current ramps up until the voltage-comparator trips and the control logic turns the switch off. Also the switch is turned off by the current limit comparator in case the current limit of the P-channel switch is exceeded. After the dead time preventing current shoot through, the N-channel MOSFET rectifier is turned on and the inductor current ramps down. The next cycle is initiated by the clock signal again, turning off the N-channel rectifier and turning on the P-channel switch. The error amplifier as well as the input voltage determines the rise time of the saw tooth generator; therefore, any change in input voltage or output voltage directly controls the duty cycle of the converter giving a very good line and load transient regulation. Constant Frequency Mode Operation (SYNC = HIGH) In the constant frequency mode, the output voltage is regulated by varying the duty cycle of the PWM signal in the range of 100% to 10%. Connecting the SYNC pin to a voltage greater than 1.5 V forces the converter to operate permanently in the PWM mode even at light or no load currents. The advantage is the converter operates with a fixed switching frequency that allows simple filtering of the switching frequency for noise sensitive applications. In this mode, the efficiency is lower compared to the power-save mode during light loads (see Figure 17). The N-MOSFET of the devices stays on even when the current into the output drops to zero. This prevents the device from going into discontinuous mode. The device transfers unused energy back to the input. Therefore, there is no ringing at the output that usually occurs in the discontinuous mode. The duty cycle range in constant frequency mode is 100% to 10%. It is possible to switch from forced PWM mode to the power-save mode during operation by pulling the SYNC pin low. The flexible configuration of the SYNC pin during operation of the device allows efficient power management by adjusting the operation of the TPS6205x to the specific system requirements. Power-Save Mode Operation (SYNC = LOW) As the load current decreases, the converter enters the power-save mode operation. During power-save mode the converter operates with reduced switching frequency in PFM and with a minimum quiescent current to maintain high efficiency. Whenever the average output current goes below the skip threshold, the converter enters the power-save mode. The average current depends on the input voltage. It is 100 mA at low input voltages and up to 200 mA with maximum input voltage. The average output current must be below the threshold for at least 32 clock cycles (tcy) to enter the power-save mode. During the power-save mode the output voltage is monitored with a comparator. When the output voltage falls below the comp low threshold set to 0.8% above VO nominal, the P-channel switch turns on. The P-channel switch turns off as the peak switch current of typically 200 mA is reached. The N-channel rectifier turns on and the inductor current ramps down. As the inductor current approaches zero, the N-channel rectifier is turned off and the switch is turned on starting the next pulse. When the output voltage can not be reached with a single pulse, the device continues to switch with its normal operating frequency, until the comparator detects the output voltage to be 1.6% above the nominal output voltage. The converter wakes up again when the output voltage falls below the comp low threshold. This control method reduces the quiescent current to typically to 12 µA and the switching frequency to a minimum achieving the highest converter efficiency. Having these skip current thresholds 0.8% and 1.6% above the nominal output voltage gives a lower absolute voltage drop during a load transient as anticipated with a standard converter operating in this mode. Feedforward Capacitor The feedforward capacitor, C(ff) shown in Figure 21, improves the performance in SKIP mode. The comparator is faster, therefore, there is less voltage ripple at the output in SKIP mode. Use the values listed in Table 2. Larger values decrease stability in fixed frequency PWM mode. If the TPS6205x is only operated in fixed frequency PWM mode, the feedforward capacitor is not needed. 10 Submit Documentation Feedback Copyright © 2002–2011, Texas Instruments Incorporated Product Folder Links: TPS62052 TPS62054 TPS62056 TPS62050 TPS62051 |
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